Hydraulic fracturing, also commonly referred to as “hydrofracking,” is a technique used in the removal of oil and natural gas from reservoirs contained in subsurface rock formations. Hydraulic fracturing works by increasing the pressure in the formation rock so that fractures form, creating a pathway through which oil and gas can travel to the well bore. Hydraulic fractures are typically created by pumping a fracturing fluid into a wellbore at a rate sufficient to increase the pressure downhole to an amount that exceeds the fracture strength of the formation rock. The increased pressure due to the high-pressure pumping of the fracturing fluid causes cracks to form in the formation rock. The fracturing fluid can then enter the cracks and extend the cracks further into the formation. Solid proppant is typically added to the fracture fluid to keep the cracks open.
The solid proppant is often a silica containing material, such as silica sand or resin coated silica sand. Large amounts of dust are created and released into the atmosphere when proppant is prepared for use in the hydrofracking process. During preparation, large amounts of proppant are trucked into the drill site by pneumatic tankers. The proppant is then blown from the pneumatic tanker into proppant storage trailers (more generally, storage vessels) sometimes referred to as “sand chiefs,” “sand hogs,” “sand kings,” “mountain movers,” or “frac sanders.” The top of the proppant storage trailers incorporate a series of vent hatches that vent pressurized air as the proppant is pumped into the storage trailer. As the air is vented through the top of the storage trailer, large amounts of silica-containing dust blow out the vent hatches. The flow of dust through the vent hatches creates large dust clouds when storage trailers are filled with proppant. The dust clouds obscure vision and may create an inhalation hazard for workers at the well site.
After proppant is loaded into the storage trailer, it is then used in the fracking process. In a typical arrangement, proppant flows out of valves on the bottom of the trailer onto a conveyor belt that is underneath the trailer. The proppant next flows onto a “stinger” or “t-belt,” which are moveable conveyor belts that lift the proppant onto a sand blender or “pod” machine. The sand blender receives the dry proppant into a hopper at the rear of the machine (the “pod hopper”) and then blends it into a slurry having constituent components such as water, sand, dry chemicals and liquid chemicals to provide the desired fracturing fluid. The slurry is pumped to the fracking well site. The flow of proppant into the sand blender pod hopper from the storage trailer creates large amounts of silica dust.
Presently, one method for reducing the flow of dust through the storage trailer vent hatches is use of a loose-fitting fabric filter bag that is attached to the access door. The fabric filter bag is shaped like a garbage bag that inflates with air and stands upright when proppant is loaded onto the storage trailer. The fabric filter bags are undesirable because the loose fit often causes the filter bag to be completely or partially blown off the vent hatch, allowing large amounts of dust to escape. The bags are also easily blown off the vent hatch because the bag stands upright when inflated.
The use of the loose-fitting fabric filter bags is disfavored because the bags make it impossible for workers to look down into the vent hatch to monitor the amount of proppant being pumped into the storage trailer. Because of the drawbacks of the loose-fitting fabric filter bags, employees of many hydrofracking operations choose to use no filter device on proppant storage trailer vent hatches, allowing large amounts of dust to be emitted.
Additionally, there is no easily feasible method for limiting the large amounts of dust that are generated when proppant drops onto the conveyor belt and is transferred from the storage trailer onto the sand blender. One current method for reducing the dust involves the placement of metal manifolds near the conveyor belt and other pieces of fracking equipment. The metal manifolds are vacuum via a system of ducts, and negative pressure generated by the vacuum removes some of the dust generated during the proppant transfer. This method is undesirable because it requires a large amount of vacuum to generate enough negative pressure to “suck up” the dust, and it requires constant monitoring of the system to remove the dust. Additionally, it collects large amounts of proppant which can then be re-incorporated into the fracking process.
Accordingly, there remains a need for a filtering system that may be easily used to minimize or prevent the emission of silica dust particles during the preparation of proppant for hydraulic fracturing.